There is a wide variety of electric switching circuits for applications in which the malfunction of the switching arrangements frequently result in serious damage to the principle and/or auxiliary equipment and/or products or processes controlled by those switching circuits.
A pertinent application in point is circuitry commonly used in generating rotating magnetic fields in magnetic bubble storage systems. Here a pair of electromagnets are arranged at right angles to each other. Rising and falling magnetic fields interact to form a rotating magnetic field. Those varying magnetic fields are generated by switching current into and out of the electromagnets. In practice, switching transistors are used. An example of practical circuitry to which the invention is applicable is found in the copending U.S. patent applications Ser. No. 162,294 of Dale Keith Jadus and Richard Owen Seeger, filed on June 23, 1980 for "Current Switch Driving Circuitry", and Ser. No. 162,293 of Fred Andrew Perner and Lionel Daniel Provazek, filed on the same day for "Current Switch Driving Circuit Arrangements". While the reliability of such switching transistors is high, failures do occur, and when they do, serious and sometimes catastrophic losses result.
Efforts have been exerted for detecting the possiblility of such failures and countering the effects that follow. For the most part, these prior art approaches have been too complex, and therefore too costly, and too critical in adjustment for the degree of reliability required.